linux-kernel - Re: [PATCH RFC v2 bpf-next 9/9] selftests/bpf: Add iter_task_vma

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Date:   Wed, 8 Mar 2023 15:00:02 +0100
From:   Jiri Olsa <olsajiri@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Hao Luo <haoluo@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Matthew Wilcox <willy@...radead.org>, bpf@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Namhyung Kim <namhyung@...il.com>
Subject: Re: [PATCH RFC v2 bpf-next 9/9] selftests/bpf: Add
 iter_task_vma_buildid test

On Tue, Mar 07, 2023 at 05:32:17PM -0800, Andrii Nakryiko wrote:

SNIP

> > diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task_vma_buildid.c b/tools/testing/selftests/bpf/progs/bpf_iter_task_vma_buildid.c
> > new file mode 100644
> > index 000000000000..dc528a4783ec
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/bpf_iter_task_vma_buildid.c
> > @@ -0,0 +1,60 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include "bpf_iter.h"
> > +#include "err.h"
> > +#include <bpf/bpf_helpers.h>
> > +#include <string.h>
> > +
> > +char _license[] SEC("license") = "GPL";
> > +
> > +#define VM_EXEC                0x00000004
> > +#define D_PATH_BUF_SIZE        1024
> > +
> > +struct {
> > +       __uint(type, BPF_MAP_TYPE_HASH);
> > +       __uint(max_entries, 10000);
> > +       __type(key, char[D_PATH_BUF_SIZE]);
> > +       __type(value, struct build_id);
> > +} files SEC(".maps");
> > +
> > +static char path[D_PATH_BUF_SIZE];
> > +static struct build_id build_id;
> > +
> > +SEC("iter/task_vma")
> > +int proc_maps(struct bpf_iter__task_vma *ctx)
> > +{
> > +       struct vm_area_struct *vma = ctx->vma;
> > +       struct seq_file *seq = ctx->meta->seq;
> > +       struct task_struct *task = ctx->task;
> > +       unsigned long file_key;
> > +       struct inode *inode;
> > +       struct file *file;
> > +
> > +       if (task == (void *)0 || vma == (void *)0)
> > +               return 0;
> > +
> > +       if (!(vma->vm_flags & VM_EXEC))
> > +               return 0;
> > +
> > +       file = vma->vm_file;
> > +       if (!file)
> > +               return 0;
> > +
> > +       __builtin_memset(path, 0x0, D_PATH_BUF_SIZE);
> > +       bpf_d_path(&file->f_path, (char *) &path, D_PATH_BUF_SIZE);
> > +
> > +       if (bpf_map_lookup_elem(&files, &path))
> > +               return 0;
> > +
> > +       inode = file->f_inode;
> > +       if (IS_ERR_OR_NULL(inode->i_build_id)) {
> > +               /* On error return empty build id. */
> > +               __builtin_memset(&build_id.data, 0x0, sizeof(build_id.data));
> > +               build_id.sz = 20;
> 
> let's replace `#define BUILD_ID_SIZE_MAX 20` in
> include/linux/buildid.h with `enum { BUILD_ID_SIZE_MAX = 20 };`. This
> will "expose" this constant into BTF and thus vmlinux.h, so we won't
> have to hard-code anything. BPF users would be grateful as well.
> 
> No downsides of doing this.

ok works nicely.. thanks

jirka